Heretofore, the three-phase alternating current generator winding and load connection used conventionally and generally Y-connection in high-voltage circuits, Δ-connection in low-voltage circuits and combinations of Y-delta or delta-Y in higher harmonic processing circuits.
Incidentally, the method used for a high-voltage resistor circuit for this type of dry-type high-voltage resistor circuit consisted of connecting in parallel a plurality of three-phase resistor circuits consisting of Y-connection of resistor array phases in which approximately ten high-voltage resistor elements such as those having a dielectric strength of 2,000V for 1 minute at a rated voltage of 400V are connected in series to address to the working voltage of 6,600V for adjusting power consumption, of arranging approximately one hundred and fifty resistor elements of one electric phase in a vertical rectangular frame box and cooling the group of resistor elements by an air blower to radiate heat. And the typical examples are disclosed in the following patent documents.                Japanese Patent Laid-open No. 6-34725        Japanese Patent Laid-open No. 7-43436        Japanese Patent Laid-open No. 9-15307        Japanese Patent Laid-open No. 9-15308        Japanese Patent Laid-open No. 9-15309        Japanese Patent Laid-open No. 2000-19231        
Specifically, traditionally a high-voltage resistor apparatus used in load characteristic tests of high-voltage generating systems including resistor elements 1 having a fin 9 shown in FIG. 15 has been used. Additional information regarding this figure is that 2′ is an outer tube in a cylindrical shape, which is formed to be approximately 1 m long.
And numeral 3 denotes a resistive heat-generating wire; numeral 4 an electrode rod, and numeral 5′ an insulating material filling up the space between the resistive heat-generating wire 3, electrode rod 4 and the internal wall of the outer tube 2′ and sealed with an end sealing member 6. This insulating material 5′ is powdery and has a function of insulating the outer tube 2′ and the resistive heat-generating wire 3 with the electrode rod 4.
Numeral 7 denotes a connection terminal fixed on both sides by nuts 8, 8 inserted on an outer end threaded portion 4a of the electrode rod 4. The resistor element 1′ is further connected with the other adjoining resistor elements 1′ through this connection terminal 7. Numeral 9 denotes a fin as described above and plays the role of a radiating plate that radiates heat generated when the resistive heat-generating wire 3 is supplied with power. The fin 9 is spirally integrally molded with or fixed on the sheath in the longitudinal direction on the periphery at intervals of approximately 7 mm.
This resistor element 1′ is made to a specification of dielectric strength 2,000 V for 1 minute at a rated voltage of 400 V to address to a working voltage of 6,600 V.
FIG. 16 shows one phase resistor array 10′ consisting of the resistor elements 1′ connected in series. Numeral 11 denotes a connection member which connects the adjoining resistor elements 1′ in the place of the connection terminal 7. Numeral 12′ denotes a rectangular frame box being disassembable. The arrangement board 12a′ of the rectangular frame box 12′ holds ten resistor elements 1′, the both ends of which penetratingly bridge the arrangement board 12a′ and constitute a resistor array 10′. Three phases of the resistor array 10′ are Y-connected to constitute the three-phase resistor circuit described below.
FIG. 17 shows a schematic structure of the high-voltage resistor apparatus γa′. The high-voltage resistor apparatus γa′ houses vertically fifteen multiple stages of the resistor array 10′ described above bridging, and five three-phase resistor circuits 17 are combined in parallel to form a lower-capacity configuration bank 13′ constituting a lower-capacity high-voltage resistor circuit βa′.
At this time, adjoining upper and lower horizontal stages of resistor elements 1′ are staggered so that the fins 9 of the resistor elements 1′ may not overlap mutually. This is because airstream cooling from below by the cooling fan described below must be carried out evenly all over the entire space due to quite a high temperature that results from various resistor elements being activated with power switched on.
In the figure, numeral 15 denotes a first terminal plate. It is connected with the input line 16 from the high-voltage generating system to be tested, and also connected by the connecting line 18 with one end three-phase of the three-phase resistor circuit 17 of each Y-connection that had been bridge connected in multiple stages. Numeral 19 denotes a second terminal plate that serves as the common neutral point connecting all the three-phase resistor circuits 17 of each Y-connection with connecting lines 20 so that the other end of the three-phase resistor circuit 17 of each Y-connection may be zero phase.
An embodiment wherein the lower-capacity configuration bank 13′ bridge held in the rectangular frame box 12′ includes the cooling fan 14′ described above is shown in FIG. 18. In the figure, numeral 21 denotes a vibration-proof rubber, and numeral 22 an insulator for insulating the rectangular frame box 12′ from the fixing frame F (see FIG. 17). The addition of this insulator 22 works to further enhance the insulation of the whole rectangular frame box 12′. In the figure, numeral 23 denotes a hood, and 24′ an air blower.
And the dry-type high-voltage load system circuit Ε′ of FIG. 19 shown in Japanese Patent Laid-open No. 5-215825 is constituted by a high-voltage resistor apparatus γa1′-γan′ with an air blower 24′ constituted by a plurality of lower-capacity configuration banks 13′ and a variable low-voltage resistor apparatus 26 having an air blower 24′ constituted by lower-capacity configuration banks 13′ through a transformer 25 are connected in parallel with a high-voltage power generator G, and the lower-capacity high-voltage resistor circuit βa′ having an air blower 24′ is constituted by lower-capacity configuration banks 13′ each having an air blower 24′ bridge held in each rectangular frame box 12′.
Accordingly, when dry-type high-voltage load system apparatuses δ′ are loaded on the loading platform 27a of an autotruck 27 shown in FIG. 20(a) and FIG. 20(b), the number of resistor elements 1′ is limited for the dimensions of the rectangular frame box 12′ because resistor elements 1 each having a bulky fin 9 are bridge held, and as a result we were forced to divide the apparatus into a plurality of lower-capacity configuration banks 13′ (eleven units in the figure). And as a natural consequence the dimensions of the autotruck 27 had to be made larger. In FIG. 19, numeral 28 denotes a load switching portion, βb′ a lower-capacity low-voltage resistor circuit, and in FIG. 20(a), 29 a control room, and 30 an appliance room.
As a result of load characteristic tests conducted in a high-voltage power generator G by using a large number of conventional dry lower-capacity configuration banks 13′ divided into small lots, the temperature of air-cooled lower-capacity configuration banks soared as high as 140 degrees C., and it was found that individual units of resistor elements 1′ had a temperature ranging from 350 degrees C. to 700 degrees C.
This is because, although the fins 9 of the resistor elements 1′ for a high-voltage use arranged in the resistor array 10′ are staggered to avoid their overlapping in the vertical direction, the shape of this fin 9 impedes the circulation of air generated by the air blower 24′, and heat accumulates within the rectangular frame box 12′ canceling the cooling action of the cooling fan 14′. The fin 9 the presence of which is considered as a common sense in this high-voltage resistor element 1′ for the high-voltage use is very effective in low-voltage resistor elements. However, it has not been clearly understood that it causes various disadvantages stated below.
Specifically, the fin 9 that impedes the circulation of air causes air turbulence or disrupts the circulation of air within the rectangular frame box constituted by lower-capacity configuration banks 13′ of the high-voltage resistor apparatus γa. As a result, the phenomenon of causing vibrations cannot be avoided, and in the conventional embodiment shown in FIG. 18, vibration-proof rubbers 21 are used to avoid the transmission of vibrations to the fixture frame F of the rectangular frame box 12′. However, the rectangular frame box 12′ itself keeps on vibrating and the risk cannot be wiped out during tests.
Moreover, as the insulating material 5′ contained in the outer tube 2′ of the resistor element 1 is powdery, it is impossible to coat evenly because the insulating material moves and concentrates on one side due to external vibration, and the resulting partially inadequate insulation not only triggered dielectric breakdown, but also the powdery insulating material led to many shortcomings such as causing the red hot resistive heat-generating wire 3 in operation to vibrate easily, becoming liable to disconnect and insufficient thermal insulation capacity. Nevertheless, the cause of arc discharges and chaining disconnection accidents resulting from dielectric breakdown has been taken in the past as resulting from faulty operations of the operator and has not been fully analyzed.
And the shape of the fin 9 as shown in FIG. 15 is designed to facilitate the radiation of heat. Due to its pointed tip, however, at high voltage, corona discharges begins to occur at the sharp edge 9a, 9a and finally arc discharges occur between rectangular frame boxes 12′ or mutually between fins 9 of resistor elements 1′ of three-phase resistor circuits 17 arranged in parallel, causing dielectric breakdown. Many years of experiment have finally led to the discovery of this fact. And it has been impossible to use the conventional resistor elements 1′ to carry out load characteristic tests without running any risk.
As a safety measure against possible dielectric breakdown of a rectangular frame box 12′ due to arc discharges, insulators 22 are provided. However, as the high-voltage overcurrent is cut off from any means of escape, the whole high-voltage resistor apparatus γa′ runs the risk of a burnout breakdown, and the workers cannot approach the same during the operation of the apparatus due to a high risk.
In addition, due to the blocking of staggered fins 9, it is difficult to obtain a perspective view from the above of the inside of the rectangular frame box 12′ and this impeded maintenance, inspection and servicing work. Moreover, as the presence of the fins 9 impeded the work of pulling out only burned out or disconnected resistor elements 1′ from the rectangular frame box 12′, any partial replacement of resistor elements 1′ is impossible at the site of the operation. Therefore, rectangular frame boxes 12′ must be brought back to the factory every time, disassembled and removed other resistor elements 1′ and the problem parts had to be replaced. For this reason, load characteristics tests had to be interrupted and delayed.
This arc discharge dissuades us from carrying out any test operations (Japanese Patent Laid-open No. 2000-19231, p (3) 0013-14). Any major failure of the high-voltage resistor apparatus γa′ due to arc discharges leads to melting and welding in a horrible shape of a plurality of resistor elements 1′, electric wires (input lines 16, connecting lines 18, 20), the first and second terminal plates 15, 19 and the rectangular frame box 12′ and to the burnout breakdown of insulators 22.
Even if anyone tries to observe the initial phenomenon of a failure, approximately one hundred and fifty resistor elements 1′ are housed in a rectangular frame box 12′ to be used at a high voltage the sides of which are covered. Thus, it is impossible to peek at the inside, and any attempt to observe anything deep inside by means of a fiberscope is foiled by a high voltage. By looking at the remnant of a burnt high-voltage resistor apparatus γa′, it was extremely difficult to determine the cause, whether it was due to insufficient cooling or whether arc discharge occurred in a very short period of time after the initial failure.
Here, we will explain on the possible impact of the disconnection of a single resistor element 1′ on chaining disconnection, when three-phase connecting lines 20 are used to connect in common the neutral point N on the second terminal plate 19 in order to realize Y-connections of resistor arrays 10′ by the group of three stages in a high-voltage resistor apparatus γa′. This chaining disconnection generates unbalanced potentials at the neutral point N and reduces the capacity of the high-voltage resistor apparatus γa′.
Here, the three-phase resistor circuit 17 of three phase 6,600V and 750 kW is constituted by a total of four hundreds and fifty resistor elements 1′ of 1.67 kW each, each three-phase constituted by connecting in parallel fifteen stages of resistor array 10′ constituted by connecting in series ten resistor elements 1′ in one phase, and each three phases being Y-connected. When this is shown by equivalent circuits of the three-phase resistor circuit 17 of FIG. 21, the result will be an equivalent potential disposition of the R phase shown in FIG. 22 and the Y series equivalent circuits of the lower-capacity high-voltage resistor circuit βa′ shown in FIG. 23.
By assuming various fault phases between the array phases R-N as shown in FIG. 24, we will examine changes in the sound array phases S-N and T-N. Even in a balanced state between the three-phase voltage on the source and the three-phase parallel resistance value of the load, due to intermittent heating as in the case of speed governor test or heating for long hours as in the case of rated load operation, the resistor elements 1′ whose resistance value is high or whose combination with cooling condition is inappropriate are first to deteriorate and to break.
The entire resistor array 10′ of which a single resistor element 1′ has been broken ceases to function (broken wire array phase). The parallel resistance value of the R array phase including a broken wire array phase is greater than sound S and T array phases. Accordingly, the voltage between R-N is higher than S-N and T-N according to a given principle. The equivalent circuits are shown respectively for R array phase one line broken in FIG. 24, for the potential rise by line broken in FIG. 25(a) and for the different potential disposition in FIG. 26.
6600/√3=3810V will be 6600√3/2=5715V.
This rise in voltage increases the heat generated by the group of resistor elements 1′ of the sound array phases Nos. 2-15 (sound array phases #2-#15) remaining in R array phase and induces the wire rupture of the second adjoining resistor element 1′ arranged in parallel. And increases in voltage of the third, fourth and other groups of resistor elements 1′ accelerates the rupture of wire (chain breaking), and the voltage between R-N at the time when remaining array phases Nos. 2-15 of the R array phase cease function rises to 5,715 V. This chaining disconnection occurs earlier as the capacity of the lower-capacity high-voltage resistor circuit βa is smaller, and turns the R array phase a fault lower-capacity high-voltage resistor circuit (βa′) (see FIG. 25(a)).
A three-phase 216 kW lower-capacity high-voltage resistor circuit βa with R fault phase turns into a single-phase 375 kW between S-T. It generates an unbalanced load and a general decline of capacity (capacity shortage) of the high-voltage resistor apparatus γa′. On the other hand, it becomes difficult to secure a number of combinations of three-phase resistor circuits 17 corresponding to the target value.
And as FIG. 25 (b) shows, potential rises in case of a short-circuit between R-N, and the voltage between R-N during a short-circuit falls close to zero. As a result, the voltage of sound array phases S-N and T-N rises close to 6,600 V. This rise in voltage induces chain breaking in resistor elements 1′ of the sound array phases S-N and T-N. Resistor elements 1′ with a withstand voltage of 2,000 VAC for 1 minute cannot be guaranteed against any dielectric breakdown after the passage of one minute.
As each high-voltage resistor apparatus γa′ is insulated by insulators, neither ground relay nor overcurrent relay works even if arc discharges occur between resistor elements 1′ and connection terminal 7 or rectangular frame boxes 12′, and the resulting damages expand.
When the neutral point N of other three-phase resistor circuits 17 are connected in common with the second terminal plate 19 as the connecting lines 20 shown in FIG. 17, any increase in the potential of the three-phase resistor circuit 17 with a fault phase spreads to other sound three-phase resistor circuits 17 connected in parallel thereto. A three-phase resistor circuit 17 having a dormant resistor array 10′ and other sound three-phase resistor circuits 17 connected in parallel thereto acquire different potential disposition, and here again the fins 9 form an environment for discharges.
The shape of each fin 9 is nearly circular as seen from the axial direction. When viewed from its side, however, the circumferential edge of a thin plate constitutes a sharp edge 9a (see FIG. 15). At high voltage, the sharper the edge, the more liable to discharge, and the sharp edges 9a of fins 9 constitute areas susceptible of inducing discharges. In a lower-capacity high-voltage resistor circuit βa, they play a role of reducing the voltage for starting discharges, and discharges occur when the following different potential disposition is in place.
A high-voltage resistor apparatus γa having one array phase for each stage of a rectangular frame box 12′ connects the R array phase of the high-voltage power generator G with the first terminal plate 15 and uses the second terminal plate 19 as the neutral point (node). Vertically stages Nos. 1-15 (#1-#15) of the resistor array 10′ are connected in parallel, each resistor array 10′ being constituted by a row of resistor elements 1′ connected in series and numbered 1-10 (#1-#10) from the left to the right for each stage. The potential difference between resistor elements 1′ connected in series is a difference of 381 V when they are sound, and the potential difference between the resistor elements 1′ connected in parallel is zero. They constitute an equivalent potential disposition and are stable (see FIG. 22).
Supposing that a resistor element 1′ of the resistor array 10′ (for example, #10 on the stage No. 1) is broken, and the R side is maintained at 3,810 V and the neutral point N is kept at zero V. A comparison of the distribution of potential in this state reveals that the voltage of 3,810V on the R side extends to all the #1-#9 on the first stage. Between #9 on the first stage and the adjoining resistor element 1′, a difference of potential of close to 3,174V develops constituting a different potential disposition (see FIG. 26). It should be noted in this connection that the breakdown of the resistor element 1′ does not necessarily occur between the order Nos. 5-6.
Although it is difficult to find out the starting point of discharge from the trace of meltdown due to arc discharges, it is possible to observe corona discharge by raising gradually voltage in a dark room by taking note of the fact that initial discharges begin with a corona. Initial corona discharges do not induce meltdown, and the discharge point can be easily identified. On the resistor element 1′ side, the cut end of the sharp edge 9a of fins 9 or burrs or dusts that have attached thereon serve as the starting point for discharges. The other side tends to fall preferably on far-away protrusions than flat plates nearby.
A fin 9 having a sharp edge starts discharges between fins 9 in case of the breakdown of a resistor element 1′. As a chain reaction to this, discharges occur between the connection terminal 7 on both ends of a resistor element 1′ and metal outer tube 2′. It is impossible to prevent discharges from fins 9 due to different potential disposition even if insulating materials are used on the rectangular frame boxes 12′.
In a conventional high-voltage resistor apparatus γa, it was impossible to clarify the chain breaking that occur when weak insulation and the neutral point N of three-phase resistor circuits 17 constituted by the Y-connection of resistor array 10′ are connected in common and the ill effect of discharge characteristic of fins 9 extends successively when one of the resistor elements 1′ is broken. Accidents resulting from these ill effects tended to be considered simply as the results of faulty operations.
And in case where Δ-connection without common neutral point N is adopted in a high-voltage resistor apparatus γa′, no chaining disconnection due to common neutral point N occurs. However, it is impossible to prevent chain breaking due to arc discharges between parallel resistor elements 1′ and arc discharges between a resistor element 1′ and an arrangement board 12a′. 
In addition, due to the employment of resistor elements 1′ each having fin 9, one lower-capacity configuration bank 13′ has to be bridge held by one rectangular frame box, and therefore a large number of sub-divided lower-capacity configuration banks 13′ are necessarily required as compared with the dry-type high-voltage load system apparatus δ′. In addition, an air blower 24′ must be fitted on each lower-capacity configuration bank 13′ increasing the initial cost (production cost) and running cost. On top of this, housing facilities and autotrucks 27 for housing and mounting the dry-type high-voltage load system apparatus δ′ become large, the former requiring a large area for installing and the latter being restricted by the width of traffic roads leading to and parking space at the site.
The major objects of the present invention are as follows:
A first object of the present invention is to provide a dry-type high-voltage load system apparatus constructed to be strong against chain breaking and arc discharges and a method of preventing chain breaking and arc discharges on the same apparatus.
A second object of the present invention is to provide a dry-type high-voltage load system by adopting a compact resistor element of a special construction for its high-voltage resistor circuit element and a method of preventing chain breaking and arc discharges on the same apparatus.
A third object of the present invention is to provide a dry-type high-voltage load system apparatus having a high-voltage load system circuit resistant against vibrations, arc discharges and chain breaking and a method of preventing chain breaking and arc discharges on the same apparatus.
A fourth object of the present invention is to provide a dry-type high-voltage load system apparatus wherein a compact high-voltage load system circuit can be formed and a method of preventing chain breaking and arc discharges on the same apparatus.
A fifth object of the present invention is to provide a dry-type high-voltage load system apparatus wherein a high-voltage bank and a low-voltage bank can be bridge held respectively in two vertical rectangular frame boxes or both of them in a horizontal rectangular frame box and a method of preventing chain breaking and arc discharges on the same apparatus.
A sixth object of the present invention is to provide a dry-type high-voltage load system apparatus wherein the housing facilities for housing and mounting the high-voltage load apparatus and the autotrucks for loading and housing the same can be made smaller and a method of preventing chain breaking and arc discharges on the same apparatus.
Other objects of the present invention will be automatically obvious from the descriptions of the specification, drawings and especially claims hereof.